In a conventional glass sheet forming system including a furnace having a forming section and a topside support device, a glass sheet is received by the topside support device which includes a downwardly facing surface for receiving the glass sheet prior to release onto a glass sheet shaping tool such as a lower mold used for forming the glass sheet. The glass sheet is supported on the topside support device by vacuum and pressure on the downwardly facing surface prior to being deposited onto the lower mold.
Pressurized gas is used to prevent surface-to-surface contact and to assist in conveying the glass sheet. Inertia of the glass sheet moving in a plane of conveyance in the furnace provides movement of the glass sheet supported on the topside support device into engagement with a suitable mechanical stop mounted on the topside support device. The pressurized gas stream can be inclined to assist the inertia in conveying the glass sheet to engagement with the mechanical stop. A back gate assembly is moved into position at the upstream end of the glass sheet to prevent it from bouncing off the mechanical stop. With the glass sheet so positioned, the vacuum drawn by the topside support device is terminated and the glass sheet is deposited on the lower mold below the topside support device.
The lower mold is then shuttled into the forming section wherein an upper mold, having a downwardly facing shaping surface, engages with the glass sheet on the lower mold imparting a shape to the glass sheet. This system incurs alignment problems as components of the apparatus heat up and undergo thermal expansion. These alignment problems occur at the interface of the topside support device and lower mold and also at the interface of the lower mold and upper mold, resulting in incorrectly formed glass sheets.
To lessen these alignment problems, a plurality of locators as taught in U.S. Pat. No. 4,877,437 are mounted on the lower mold for accurately registering the glass sheet deposited from the topside support device on the lower mold. However, such tooling is expensive and requires high maintenance. Also, because such tooling and support structure are subjected to thermal gradients, the same undergoes thermal expansion and contraction that results in misalignment in the forming section at the interface of the upper and lower molds during engagement thereof.